SUNRPC: Check rq_auth_stat when preparing to wrap a response

Commit 5b304bc5 ("[PATCH] knfsd: svcrpc: gss: fix failure on
SVC_DENIED in integrity case") added a check to prevent wrapping an
RPC response if reply_stat == MSG_DENIED, assuming that the only way
to get to svcauth_gss_release() with that reply_stat value was if
the reject_stat was AUTH_ERROR (reject_stat == MISMATCH is handled
earlier in svc_process_common()).

The code there is somewhat confusing. For one thing, rpc_success is
an accept_stat value, not a reply_stat value. The correct reply_stat
value to look for is RPC_MSG_DENIED. It happens to be the same value
as rpc_success, so it all works out, but it's not terribly readable.

Since commit 438623a0 ("SUNRPC: Add svc_rqst::rq_auth_stat"),
the actual auth_stat value is stored in the svc_rqst, so that value
is now available to svcauth_gss_prepare_to_wrap() to make its
decision to wrap, based on direct information about the
authentication status of the RPC caller.

No behavior change is intended, this simply replaces some old code
with something that should be more self-documenting.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/auth_gss/svcauth_gss.c

@@ -1732,17 +1732,19 @@ svcauth_gss_accept(struct svc_rqst *rqstp)
 }
 
 static __be32 *
-svcauth_gss_prepare_to_wrap(struct xdr_buf *resbuf, struct gss_svc_data *gsd)
+svcauth_gss_prepare_to_wrap(struct svc_rqst *rqstp, struct gss_svc_data *gsd)
 {
+	struct xdr_buf *resbuf = &rqstp->rq_res;
 	__be32 *p;
 	u32 verf_len;
 
 	p = gsd->verf_start;
 	gsd->verf_start = NULL;
 
-	/* If the reply stat is nonzero, don't wrap: */
-	if (*(p-1) != rpc_success)
+	/* AUTH_ERROR replies are not wrapped. */
+	if (rqstp->rq_auth_stat != rpc_auth_ok)
 		return NULL;
+
 	/* Skip the verifier: */
 	p += 1;
 	verf_len = ntohl(*p++);
@@ -1786,7 +1788,7 @@ static int svcauth_gss_wrap_integ(struct svc_rqst *rqstp)
 	u32 offset, len, maj_stat;
 	__be32 *p;
 
-	p = svcauth_gss_prepare_to_wrap(buf, gsd);
+	p = svcauth_gss_prepare_to_wrap(rqstp, gsd);
 	if (p == NULL)
 		goto out;
 
@@ -1846,7 +1848,7 @@ static int svcauth_gss_wrap_priv(struct svc_rqst *rqstp)
 	u32 offset, pad, maj_stat;
 	__be32 *p, *lenp;
 
-	p = svcauth_gss_prepare_to_wrap(buf, gsd);
+	p = svcauth_gss_prepare_to_wrap(rqstp, gsd);
 	if (p == NULL)
 		return 0;